English Wikipedia has an article on:

Pseudo-differential operator

Wikipedia

• pseudo-differential operator

pseudodifferential operator (plural pseudodifferential operators)

1. (mathematics) An extension of the differential operator, used in the theory of partial differential equations and quantum field theory.
   • 2009 January, Notices of the American Mathematical Society‎^[1], volume 56, number 1:

     The algebras in question come from problems in various areas of mathematics and mathematical physics; typical examples include algebras of pseudodifferential operators, group algebras, and other algebras arising from quantum field theory.